Recent years have seen widespread use of electronic equipment which can be operable by touching its screen with a finger, a pen, or the like. In a known method for detecting a touch position in a display screen, a plurality of optical sensors are provided on a display panel and used to sense a projected or reflected image formed by a finger or suchlike approaching the screen. In another known method, to detect a touch position with high accuracy for any display data, a display device is provided with an infrared backlight for emitting infrared light, and a reflected image formed by infrared light is sensed using optical sensors.
In addition to the infrared backlight, such a display device with optical sensors is provided with, for example, an A/D converter for converting signals being read from the optical sensors into digital signals and a recognition processing portion for obtaining touch positions on the basis of the resultant digital signals. Consequently, the display device with optical sensors has a problem of its power consumption being higher than display devices without optical sensors.
Therefore, in one conceivable method for reducing power consumption, the display device with optical sensors has a normal mode and a standby mode set therefor, and in the standby mode, circuits can be stopped from operating or their operation can be slowed. In relation to this, Japanese Laid-Open Patent Publication No. 2009-193482 discloses a configuration in which, when the operation mode is normal, a received optical signal for one screen is read at intervals of 60 Hz, and in a low-consumption mode (standby mode), a received optical signal for one screen is read at intervals of 10 Hz.